What is Carnitine, and Which Type is Best?

Carnitine is an amino acid that helps the body burn large fat molecules and remove cellular toxins. It is primarily used as a nutritional supplement for athletes to improve their performance, but it has many medical uses, as well. As a nutritional supplement, carnitine may help boost the rate at which you burn fat, increase your energy levels, and support nerve regeneration and sensitivity. As a medical treatment, it can help improve fat metabolism, reduce nerve pain, and alleviate certain heart and kidney conditions, among many others. What carnitine is useful for depends on your personal health and your overall goals.

First extracted from meats in 1905, carnitine is an appropriate name because it literally means “taken out of meat.” Despite the name, it is also found in plants like asparagus, although at much lower levels. It has been in use for several decades and has many clinically proven uses with only rare side effects. You will find this compound in almost every cell of the body. It is essential for energy production because, without it, large fat molecules cannot be burned. This compound doesn’t actually burn the fat. It acts as a shuttle, moving fat molecules into the mitochondria for burning, and then removing many of the waste products back out.

Carnitine and Fatloss! – Miguel Blacutt

There are six different types of carnitine supplements, and each one has different functions. Some of them have side effects, so it’s important to know what you are taking. Most forms of this compound are clinically useful. Without adequate amounts of this compound, you will feel fatigued and unable to do your best work. When you need energy and your blood sugar is low, this substance steps in to burn fat to keep your energy level high. If you’re interested to know exactly what is carnitine and how it can help you get more out of life, keep reading.

The Supplemental Uses of Carnitine

People have been using this supplement since 1985 when it was made commercially available in an over the counter (OTC) formulation. There are also medical uses for carnitine that have been clinically demonstrated and are backed by the medical community. Many more clinical and non-clinical uses are under investigation and show considerable promise. This compound is full of antioxidants and can help suppress free radicals in the blood, which are known to cause damage to cells. This cell damage can lead to cancer. Additionally, there is clinical evidence that this supplement can help with fat loss, as it promotes the burning of large fat molecules in mitochondria. Because of this, many people looking to lose weight or who need more energy choose to use this supplement. If you choose to use it for weight loss, consider combining it with other healthy fat loss tips to maximize your results.

What is carnitine?
Supplemental Uses of Carnitine (Image Source: Shutterstock)

One of the effects of carnitine metabolism is nitrous oxide production, which acts as a vasodilator on blood vessels. When the arteries relax and expand, blood carries more oxygen to the muscles and washes away more waste. This potentially improves athletic performance.

Exercise enthusiasts and people who expect high levels of performance from their bodies also use this supplement, and they report that carnitine supplementation can provide:

  • Improved endurance
  • Reduced muscle fatigue
  • Enhanced brain function 
  • Mild antidepressant effects 
  • Reduced use of glycogen during training
  • Increased fat metabolism

Despite all of its potential, this substance has not been well studied as a supplement. As a result, many of its potential benefits are not well defined. What we do know is that, after almost 40 years of use in clinical and non-clinical settings, serious side effects have been rare. Most of the observed side effects have been in patients who already suffered from serious medical conditions. Side effects in athletes and gym enthusiasts have been mild and rare. Dietary supplementation of carnitine results in much higher blood levels than from regular dietary consumption, so more research is needed.

The Medical Uses of Carnitine

Some of the medical value is directly related to metabolism. For some uses, however, the reason is not so clear. I have collected a sample of the many diseases that are treated with this supplement.


Low levels of this compound in bodily fluids are directly related to male infertility, so it is possible that carnitine supplementation treats infertility. It appears that, in some cases, carnitine helps women ovulate. Women with polycystic ovarian syndrome occasionally do not respond to standard therapy. This supplement may help women ovulate and increase their chances of pregnancy.


Patients with diabetic neuropathy experience more nerve regeneration and better insulin responses when they take supplemental carnitine. It also appears to relieve symptoms of metabolic syndrome, of which diabetes is a part.

Cardiovascular Disease

Carnitine treats heart disease and atherosclerosis because it helps support proper heart function. It releases nitrous oxide, which smooths and relaxes blood vessels, increasing their flexibility and volume. There is some counter evidence that suggests this compound may make atherosclerosis worse, but follow-up studies indicated that carnitine protects against atherosclerosis. Further study is necessary to discover what damage, if any, this substance may do to arteries, but as of now it is considered non-harmful.

L-Carnitine In The Secondary Prevention of Cardiovascular Disease – Mayo Proceedings

Mitochondrial Dysfunction

Many chronic and conditions of unknown origin result in a decline of mitochondrial function. Carnitine to combat fatigue is often included in therapies to increase the energy levels and fat burning capability in patients who experience mitochondrial dysfunction.


Patients suffering from the AIDS virus often experience lipodystrophy syndrome. Symptoms include insulin resistance, high concentrations of fat in the blood, and the abnormal distribution of fat around the body. AIDS is also characterized by a drop in critical immune system cells.

Evidence suggests that supplementation with carnitine helps improve the insulin response while lowering the fat concentration in the blood. It also improves mitochondrial function in AIDS patients.

Where to Find Carnitine

Your liver and kidneys are the primary sources of carnitine used by your body. It is made out of lysine and methionine and transported through the blood to all the cells of the body. Most people make enough of their own carnitine to keep them healthy and functioning normally.

For people who experience deficiency of this compound, who have a medical need, or who want to boost their metabolism, there are several external sources. It occurs naturally in many common foods; the highest concentrations are found in red meat.

Other foods also have significant levels of this compound, including fish, milk, and poultry. Adults who eat a lot of red meat receive between 50 and 200 milligrams per day from their diet. Vegans will normally only get about 10 milligrams. Most people fall somewhere in between.

These are some of the best dietary sources of carnitine:

  • Beef has between 85 and 250 milligrams per six-ounce serving.
  • Pork has about 50 milligrams in a six-ounce serving. 
  • A cup of milk has about 8 milligrams. 
  • Chicken will yield 4 to 8 milligrams in a six-ounce serving.
  • Cod is similar to chicken, with about 6 milligrams in six ounces. 
  • Most types of fish have some, but the amounts are variable and generally less than cod.  
  • Cheese has about 2 milligrams in 2 ounces. 
  • Asparagus, avocado, and wheat bread all have small amounts.
Assortment of meat and fish as natural sources of carnitine.
Dietary Sources of Carnitine (Image Source: Shutterstock)

Despite the low levels found in plants, vegans and vegetarians usually make enough carnitine on their own and do not suffer from deficiency. Dietary carnitine is modified by gut bacteria before it is absorbed, and it appears that vegans process it differently. As a result, vegans experience fewer potential side effects from supplementation.  For those non-meat eaters who are deficient, there are supplements made without animal products so they can get enough of this compound without changing their diet.

What is L-Carnitine, and How Does it Work?

L-Carnitine is the product of all carnitine synthesis in the human body. The other four useful forms are made by making additions to this root form. L-Carnitine is a transport protein that moves fat into the mitochondria where it is turned into energy.

L-Carnitine | How to Mobilize Fat & Enhance Brain Health – Thomas DeLauer

Fat is stored in the body in the form of long chains. When the body wants to burn fat, it turns to carnitine. Mitochondria are the powerplants of human cells. This compound makes a bridge across the mitochondrial wall and acts as a shuttle for large fat molecules that have more than 14 carbon atoms.

Once fat is on the inside of the mitochondria, it is completely burned and transformed into energy. The larger the fat molecule, the more energy will be created when it is burned. This is why people who want to lose weight prize this supplement. It is essential when you want to burn fat and create large amounts of energy.

L-Carnitine as a Dietary Supplement

People who are looking to lose weight, who need more energy, or who are suffering from specific conditions can take advantage of L-carnitine and other popular fat burning supplements. The positive effects of taking this supplement an hour before a fat loss workout is supported by several clinical studies. Patients suffering from fatigue due to renal disease, cancer, and aging take carnitine for fatigue.

L-Carnitine Side Effects

Side effects are uncommon, but on occasion, you may experience an upset stomach, heartburn, nausea, vomiting, or diarrhea. It can also make your breath smell fishy. If you have had seizures, L-carnitine might increase your chances of having a seizure, but a recent analysis of collected data found no link to seizures. While carnitine has been shown to help patients with heart disease, one study showed it increased levels of a chemical that aggravates atherosclerosis. Follow-up studies indicated that this compound protects against atherosclerosis. It may also increase the severity of symptoms related to hypothyroidism. If you are taking antibiotics, blood thinners, or thyroid hormones, consult with your doctor before taking this supplement.

What is Acetyl-L-Carnitine?

The mammalian brain is very sensitive, and exposure to blood causes irreversible damage. To protect the brain, the human body has a special membrane called the blood-brain barrier.

L-carnitine cannot cross the blood-brain barrier by itself, so it is modified and transformed into acetyl-L-carnitine. The addition of the acetyl group acts like a pass-key and allows this compound access to the brain and the central nervous system. This is the only form of this compound that can cross the blood-brain barrier, so it is considered the neurological form.

Once inside the blood-brain barrier, acetyl-L-carnitine performs its normal metabolic and waste disposal functions for the cells of the brain and central nervous system. The acetyl group, which is no longer needed as a passkey, is transformed into several components that are useful for nerve health and energy production.

Acetyl-L-Carnitine Side Effects

The side effects for acetyl-L-carnitine are the same as regular carnitine, so if you are pregnant, breast feeding, or have a serious medical condition, consult with your physician before taking it.

Possible Benefits of Acetyl-L-Carnitine

This can be used as a supplement to support individuals with the following conditions:

  • Alzheimer’s disease
  • Alcoholism 
  • Diabetic neuropathy
  • Fragile-X syndrome
  • Sciatica
  • Peyronie’s disease 

Most of these conditions are nerve-related, and research suggests that acetyl-L-carnitine helps by protecting, regenerating, and stimulating nerves.

Several meta-analyses indicate that acetyl-L-carnitine is effective at treating the symptoms of diabetic neuropathy. Symptoms include pain in nerves, joints, and bones; nerve degeneration; tingling and burning sensations; numbness; increased sensitivity; ulcers; and infections.

Not only does this substance reduce pain, further investigations have demonstrated that it promotes nerve regeneration and helps patients better detect vibrations.

Acetyl-L-carnitine also shows promise as an antidepressant. Many patients suffering from major depression have treatment-resistant depression (TRD). Clinical investigations discovered many of these patients are deficient in acetyl-L-carnitine, and supplementation made their condition easier to treat. Other forms of depression and related TRD are being investigated to see if they, too, can benefit from acetyl-L-carnitine supplementation. If you are considering this supplement, consult your doctor if you are suffering from depression or another serious medical condition. The Linus Pauling Institute recommended dose of this supplement is 500–1000 mg per day for healthy consumers.

Fast Acting L-Carnitine-L-Tartrate

Carnitine tartrate was developed specifically with athletes in mind. When combined with the tartrate molecule, L-carnitine is absorbed faster in the small intestine. This formulation also reduces muscle damage experienced during exercise and promotes healing during the recovery period after exercise. It interacts with testosterone and other hormones in the body to reduce fatigue and muscle weakness.

Because of the fast absorption rate, L-carnitine-L-tartrate is ideal for people who engage in strenuous exercise. If taken an hour before exercising, the additional carnitine will be available for use. Combine this with its demonstrated protective and regenerative effects, and you see that this is the ideal formulation for athletes.

L-Carnitine Fumarate for Heart Health

L-carnitine fumarate is a patented formulation of carnitine also known as Carnishield. It was developed to protect the hearts of cardiovascular patients. L-fumarate is an important part of the fat-burning Krebs cycle that takes place in the mitochondria. By combining carnitine and fumarate in one formula, Carnishield gives you more benefits.

As a supplement for physical fitness in healthy individuals, L-carnitine fumarate is considered safe. Many of the uses of this supplement require oversight from your primary care provider, so in most cases you should consult your physician before taking it.

L-Carnitine Fumarate Side Effects

The side effects for this supplement are the same as L-carnitine. People who are pregnant, nursing, or have a serious medical condition should consult with their physician before supplementing with L-carnitine fumarate.

Turbocharge your Carnitine with Propionyl-L-Carnitine

Propionyl-L-carnitine is primarily used to treat leg pain associated with atherosclerosis and diabetes. It transports fat into the mitochondria of the cells to produce energy. Once inside the mitochondria, the propionyl group detaches and is transformed into several new molecules that support metabolism. These molecules are produced at the same time a new fat molecule is transported into the cell. This ensures the mitochondria have the optimal ingredients necessary for fat burning and energy production.

These processes result in several beneficial effects that are specific to propionyl-L-carnitine. Nitric oxide is produced, which promotes better circulation. Free radicals are inhibited and lactic acid production is lower. These effects are thought to be responsible for the reduction in leg pain mentioned above. Performance of aerobic and anaerobic exercises can also be enhanced by propionyl-L-carnitine in ways not seen with other forms. Free radicals and lactic acid are suppressed, along with increased power output for anaerobic exercise and greater endurance for aerobic exercise. These effects were most effective for patients suffering from neuropathy, but modest improvements were also seen in healthy study participants.


D-carnitine is a bioactive form that is only made in the lab. L- and D-carnitine have the same chemical formula, but they are mirror images of each other. They look like a pair of gloves, with the L-form being the left glove and D-form being the right glove.

This D-form is toxic because it interferes with the proper function of L-carnitine. Taking D-carnitine can lead to serious side effects, so it is not recommended for consumption. It is not available for sale, and there are no known producers.

Side effects and complications of D-carnitine include:

  • Fatigue
  • Abdominal cramps 
  • Diarrhea
  • Nausea and vomiting 
  • Anemia
  • Hypoglycemia

What is Carnitine’s Role in Diet, Exercise, and Supplementation?

Carnitine is useful as a supplement for people who want to improve their metabolism. It is also useful for certain medical conditions. There are a wide number of health conditions that might be improved by taking this supplement. Patients with heart disease or diabetes are the most likely to see large benefits from this supplement.

If you think this may help your medical condition, it is vital you consult with your physician. Only trained medical personnel are qualified to determine the appropriate treatment for serious medical conditions. When approved, this supplement can have a tremendous impact and relieve a lot of pain and suffering.Many people today are taking supplements to boost their workout performance, as well as to enhance their overall wellness. Carnitine has been in use for almost 40 years, and its side effects are well understood. Because this supplement only interacts with certain medications, it can be taken by healthy people in combination with vitamins supplements without creating much concern.

The Biggest Benefit of L-Carnitine is… – Dr. Eric Berg DC

I take several supplements and have been enjoying the results of this supplement for several months now. I am very careful about what I put in my body and why, so I have invested a lot of time into studying supplements and their benefits.

The supplements I take have been chosen because they reinforce each other well and are unlikely to cause any harm. My primary goal is fat burning, so I have added L-carnitine to my regimen. I am happy with the results I am seeing, and I look forward to finding additional benefits.

There are five different types of carnitine, and your needs may be different from mine. Not all people are the same, so you should educate yourself to the possible risks and benefits of a supplement before taking it. Your choices should take into account the other supplements you take, as well as your long-term goals.

Moving Forward

This is a good supplement for people with an active lifestyle who take their nutrition and exercise seriously. It can help you burn additional fat and give a boost to your energy levels. Most athletes and gym enthusiasts who use this compound combine it with other supplements like Nowfoods Selenium to fine-tune and enhance their metabolism. Using several supplements that reinforce each other is a smart way to maximize the results of your efforts.

Which version of carnitine would be most useful for you? Talk with your doctor and choose the right formulation to help you reach your goals.